Catalytic desulphurisation of petroleum hydrocarbons



Se t. 27, 1955 F. w. B. PORTER 2,719,108

CATALYTIC DESULPHURISATION OF PETROLEUM HYDROCARBONS Filed D80. 18, 1952 11 k 10 I FEEDST AUTOFW'HNG q REA T Z HE TER HEA EQ B HyoRommN REACT R QecycLE LIME 1 HEAT EXCHAN GER i6 sum/E3 oaeoLFumzso peowoc r Inventor:

United States Patent CATALYTIC DESULPHURISATION OF PETROLEUM HYDROCARBONS Application December 18, 1952, Serial No. 326,704

Claims priority, application Great Britain December 21, 1951 3 Claims. (Cl. 196-28) This invention relates to the catalytic desulphurisation of petroleum hydrocarbons.

It is well-known to desulphurise petroleum hydrocarbons by passing them in admixture with hydrogen over a sulphur-resistant hydrogenation catalyst. The process is commonly carried out at elevated temperature in the region of 700-800 F. and at elevated pressure ranging up to 1000 lb./ sq. in. and large amounts of hydrogen are recycled to the reaction zone in order to maintain the necessary partial pressure of hydrogen therein, the amount of hydrogen recycled varying between 2000 and 4000 cu. ft./bbl. This process is commonly referred to as a hydrofining process and necessitates the provision of an extraneous source of hydrogen and the use of comparatively expensive steels in the manufacture of the plant in order to withstand the high pressure employed. More recently, a hydrocatalytic desulphurisation process has been evolved which is carried out under conditions such that the hydrogen required is obtained from the feedstock itself by controlled dehydrogenation so that the need for an extraneous source of hydrogen is obviated and furthermore, the process is carried out at a very much lower pressure, thus enabling the plant to be made of inexpensive steel. This process may be referred to as an autofining process and forms the subject of U. S. Letters Patent Numbers 2,573,726, 2,574,445, 2,574,446, 2,574,447 and 2,574,448.

Both the hydrofining and the autofining processes involve the recycling of large amounts of hydrogen-containing gases to the desulphurisation zone, since it has been shown that high hydrogen partial pressures are necessary in order to secure an economic degree of desulphurisation at reasonable space velocities. The plant must therefore include pumps and boosting equipment for maintaining the recycle rate.

It was then discovered that petroleum hydrocarbons could be efficiently desulphurised by the use of a sulphurresistant dehydrogenation-hydrogenation catalyst without the necessity of supplying hydrogen to the desulphurisation zone and without recycling any hydrogen to said zone. Thus, it was discovered that if the reaction were carried out under a pressure sufficient to maintain the feedstock substantially in the liquid phase and under controlled temperature conditions, it was possible to remove a considerable proportion of the sulphur contained in the feedstock as hydrogen sulphide from the treated product. It was thought that when the reaction was carried out under elevated pressure such that the feedstock was maintained substantially in the liquid phase, the small amount of hydrogen present in the reaction zone was sufficient to enable a substantial hydrogen pressure to be built up in the reactor, thus enabling hydrogenation of the sulphur-containing molecules to be effected. The preferred catalyst and process conditions for such a liquid phase process are set out in the specification of co-pending British application No. 13,766/ 49 and its companion copending U. S. application, Serial Number 163,660, filed ice May 23, 1950, now Patent No. 2,697,682. The process is similar to an autofining process carried out in the liquid phase without gas recycle but the process sufiers from two important disadvantages as follows:

(1) The necessity in the case of all feedstocks to provide means for removing a small proportion of the high boiling components of the product in order to avoid an unsatisfactory colour, and

(2) A tendency towards instability in the product.

It has ben discovered that a hydrogen-rich gas may be separated from the products obtained when carrying out the liquid phase process as above described, and that this gas can with advantage be employed to effect further desulphurisation of the treated product and/or to improve its colour. This discovery has led to the development of a continuous two-stage process which embodies the advantages of the liquid phase process while avoiding its disadvantages.

According to the invention, a process for the catalytic desulphurisation of a petroleum feedstock comprises passing the feedstock to a first reaction zone wherein it is contacted with a sulphur-resistant dehydrogenationhydrogenation catalyst under controlled conditions of temperature and pressure such that the feedstock is maintained substantially in the liquid phase and an amount of hydrogen is produced by dehydrogenation of naphthenes contained in the feedstock in excess of that required to convert organically combined sulphur in the feedstock into hydrogen sulphide but without effecting any appreciable change in the boiling range of the feedstock, continuously passing the products from said first reaction zone to a second reaction zone wherein they are contacted at elevated temperature and pressure with a sulphur-resistant hydrogenation catalyst, separating the products from said second reaction zone into a liquid product and a gaseous Q product rich in hydrogen, and recycling said hydrogenrich gaseous product to said second reaction zone.

The degree of further desulphurisation that may be effected in the second reaction zone depends upon the amount of hydrogen produced in the first reaction zone, and at the same space velocity of liquid feedstock in both zones, it may not be possible to effect complete desulphurisation in the second zone. Complete desulphurisation in the second zone can, however, be effected by reducing the space velocity in the second zone by increasing the size of the catalyst volume, or by similarly reducing the space velocity in the first zone or by increasing the temperature in the first zone if equilibrium for dehydrogenation has not already been reached.

It is advantageous to use in the first reaction zone a catalyst having the greatest possible dehydrogenating activity and in this connection, cobalt molybdate type catalysts containing fluorine, as described in the specifications of the co-pending British application No. 22,844/51 and its companion co-pending U. S. application, Serial Number 311,429, filed September 25, 1952, are particularly preferred. By a cobalt molybdate type catalyst is meant a catalyst essentially comprising the oxides of cobalt and molybdenum, either in the form of mixtures of said oxides or in the form of chemical compounds of cobalt, molybdenum and oxygen, either alone or incorporated with a support, such as alumina.

The process according to the present invention may advantageously be carried out in an apparatus as illustrated in the accompanying diagram.

The feedstock to be desulphurised is passed via line 10 and heater 11 into reactor A wherein it is contacted with a sulphur-resistant dehydrogenation-hydrogenation catalyst at elevated temperature and pressure. The term perature should be kept as low as possible to avoid substantial vapourisation of the feedstock and is preferably within the range 700800 F., while the pressure may be 500-1000 lb./sq. in., or more depending upon the boiling range of the feedstock. The products leaving the reactor A are passed at substantially the same pressure into the reactor B wherein they are contacted with a sulphurresistant hydrogenation-catalyst at elevated temperature and pressure which are governed by those established in reactor A. The products leaving reactor B are passed through heat exchanger 13 into a separator 14 operating under plant pressure. A gas mixture containing a high proportion of hydrogen is removed from the separator 14 via line 15 and is recycled by means of blower 16 through heater 17 in the reactor B. Liquid product containing hydrogen sulphide dissolved therein is removed from the separator 14 via line 18 and is treated in known manner for the separation of the hydrogen sulphide therefrom. The space velocity in the reactor B is adjusted by adjusting the catalyst volume so that the hydrogen produced in the reactor A is completely consumed in the reactor B.

The invention will now be described by way of example with reference to the desulphurisation of a petroleum fraction boiling up to the end of the gas oil range (350 C.) and containing 0.46% weight of sulphur.

The feedstock was passed to reactor A at a temperature of 780 F., a pressure of 500 p. s. i. ga., and a space velocity of 3.0 v./v./hr. Using a catalyst in the reactor A of the cobalt molybdate type containing both fluorine and phosphorus as ingredients, the sulphur content of the product leaving reactor A was 0.23% weight, i. e., a reduction of 50%. The gas make amounted to 50 cubic feet per barrel and contained 70% by volume of hydrogen. l t was therefore possible to arrange for a consumption of 35 cubic feet per barrel of hydrogen in the reactor B which is more than sufiicient to remove the sulphur remaining in the product passing to reactor B. With the same space velocity in both reactors A and B, substantially complete desulphurisation could be effected in the reactor B provided the hydrogen partial pressure Was maintained at 250-300 p. s. i. ga., and as the reactor B was operating under hydrofining conditions, the product had an improved colour.

According to another example, a gas oil of 1.16 per cent by weight sulphur content was passed to reactor A at a temperature of 750 F., a pressure of 500 p. s. i. ga.,

and a space velocity of 2.0 v./v./hr. of liquid feedstock. The product leaving reactor A had a sulphur content of 0.6% and there was an excess hydrogen make of 8 CF B. On processing the product and recycling the gases as described previously, through reactor B, a further 0.1% by weight of sulphur is removed. However, it is considered that the reduction of the space velocity or an increase of temperature in the first zone would probably increase the gas make if equilibrium for dehydrogenation had not been reached.

I claim:

1. A process for the catalytic desulphurisation of a petroleum feedstock, which comprises passing the feedstock to a first reaction zone wherein it is contacted with a sulphur-resistant dehydrogenation-hydrogenation catalyst under controlled conditions of temperature and pressure of about 700-800 F. and about 500-1000 lb./sq. in. such that the feedstock is maintained substantially in the liquid phase and an amount of hydrogen is produced by dehydrogenation of naphthenes contained in the feedstock in excess of that required to convert organically combined sulphur in the feedstock into hydrogen sulphide but without effecting any appreciable change in the boiling range of the feedstock, continuously passing the products from said first reaction zone to a second reaction zone wherein they are contacted under hydrofining conditions with a sulphur-resistant hydrogenation catalyst, separating the products from said second reaction zone into a liquid product and a gaseous product rich in hydrogen, and recycling said hydrogen-rich gaseous product to said second reaction zone.

2. A process according to claim 1, wherein the second reaction zone is operated at a lower space velocity of the liquid feedstock than the first reaction zone.

3. A process according to claim 1, wherein the catalyst in the first reaction zone consists of a fluorinecontaining cobalt molybdate type catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,253,308 Rosen Aug. 19, 1941 2,417,308 Lee Mar. 11, 1947 2,574,448 Docksey et al. Nov. 6, 1951 

1. A PROCESS FOR THE CATALYTIC DESULPHURISATION OF A PETROLEUM FEEDSTOCK, WHICH COMPRISES PASSING THE FEEDSTOCK TO A FIRST REACTION ZONE WHEREIN IT IS CONTACTED WITH A SULPHUR-RESISTANT DEHYDROGENATION-HYDROGENATION CATALYST UNDER CONTROLLED CONDITIONS OF TEMPERATURE AND PRESSURE OF ABOUT 700-800* F. AND ABOUT 500-1000 LB./SQ.IN. SUCH THAT THE FEEDSTOCK IS MAINTAINED SUBSTANTIALLY IN THE LIQUID PHASE AND AN AMOUNT OF HYDROGEN IS PRODUCED BY DEHYDROGENATION OF NAPHTHENES CONTAINED IN THE FEEDSTOCK IN EXCESS OF THAT REQUIRED TO CONVERT ORGANICALLY COMBINED SULPHUR IN THE FEEDSTOCK INTO HYDROGEN SULPHIDE BUT WITHOUT EFFECTING ANY APPRECIABLE CHANGE IN THE BOILING RANGE OF THE FEEDSTOCK, CONTINUOUSLY PASSING THE PRODUCTS FROM SAID FIRST REACTION ZONE TO A SECOND REACTION ZONE WHEREIN THEY ARE CONTACTED UNDER HYDROFINING CONDITIONS WITH A SULPHUR-RESISTANT HYDROGENATION CATALYST, SEPARATING THE PRODUCTS FROM SAID SECOND REACTION ZONE INTO A LIQUID PRODUCT AND A GASEOUS PRODUCT RICH IN HYDROGEN, AND RECYCLING SAID HYDROGEN-RICH GASEOUS PRODUCT TO SAID SECOND REACTION ZONE. 